The present invention relates generally to internal combustion engines in automotive vehicles and to engine start strategies for controlling the operation of the engine. More particularly, it provides a method of controlling emissions and engine operation during the period immediately following crank startup.
Today""s automotive engines must meet stringent emission standards. Automotive manufacturers are constantly seeking ways to reduce emissions in their engines in order to protect the environment, meet customer expectations, and comply with government regulations.
Most automotive engines presently employ a sophisticated control system consisting of sensors and feedback algorithms in conjunction with the engine and a catalyst converter. Oxygen sensors play a large role in present day systems that control emissions. They are used to sense oxygen in the fuel/air mixture, in exhaust manifold emissions, and in emissions from catalytic converters. Through feedback control, the output of the oxygen sensors is used to adjust various parameters to achieve better engine performance, including lowered emissions. Examples of the various parameters that can be controlled through feedback control include the amount of fuel injected into the cylinders, the fuel-to-air ratio, and spark timing.
Many automotive vehicles commonly employ an oxygen sensor generally disposed upstream of the exhaust system for sensing the oxygen level in the exhaust gas emitted from the engine. The oxygen sensor can serve to provide a feedback signal to control engine operation and adjust fuel injection to the engine to achieve good engine performance. However, some conventional oxygen sensors are required to warm up to a sufficiently high temperature before an accurate oxygen sensor reading may be obtained. Also, following an engine start, the oxygen sensor and processing devices initially may not have acquired enough information to provide adequate feedback control. Therefore, for a period of time immediately following cold start up of the vehicle engine, the oxygen sensor may not be capable of providing accurate information with which the engine may be controlled to operate to achieve low hydrocarbon emissions.
Additionally, immediately following a cold engine start, the catalyst of the catalytic converter can be ineffective since the catalyst requires a period of time to warm up to a temperature at which the catalyst can operate effectively to burn excess hydrocarbons. As a consequence, hydrocarbon emissions may initially be high due to poor burning of the excess hydrocarbons due to a low temperature catalyst. To add to the problem, an over abundance of fuel in the catalyst may further cool the catalyst, thereby requiring an extended period time for the catalyst to warm up to a sufficient operating temperature.
There is a need to control engine operation and reduce emissions during the period following engine startup and preceding the time when the oxygen sensors can warm up and begin to provide information necessary for feedback control. In many vehicles, emission control during the period following cold start and prior to warm up of the oxygen sensors is attempted, if at all, only by ballistic means that provide no feedback or learning. For example, a temperature sensor may be provided which sets the amount of fuel injection during the startup period according to the ambient temperature. Another approach is described in U.S. Pat. No. 5,809,969 to Fiaschetti. This patent describes an output combustion metric derived from engine speed, acceleration, and jerk. The output data are compared to a desired metric and the difference is used to control an amount of fuel injected.
The techniques practiced up until now have shown less emission reduction than desired during the start up period. The present invention provides a solution that better controls emissions during that period.
The strategy of the invention controls operation of an internal combustion engine in the time period before an oxygen sensor is warmed up sufficiently to provide reliable feedback measurements. It involves using a target speed-time (or event) goal, and then applying feedback, feedforward, and/or adaptive controls on the difference between the target and a measured engine speed. The target speed time (or event) can be programmed into an engine controller as a lookup table. The actual engine speed at each desired time or event can then be compared to the desired speed to obtain a difference value. Fueling, or any other speed control parameters, can be modified based on the difference value using feedback or feedforward routines to correct the measured value toward the target. The fueling or other control parameters can also be adapted for the next start based on any corrections.